Muttering colleague

[ImJustMadAboutSaffron]

My role has changed in that I work in a different area a few times a week, sometimes two whole days, sometimes a part of some days, there isn't a real pattern (everyone else WFH some days, I don't) and there's a guy in the room who mutters and talks to himself all the time. It's driving me absolutely up the wall.

I put on headphones to listen to some music whilst working to drown it out and then found he was trying to talk to me. I can't stand it!

I totally sympathise with you. I've been in my current role for several months but the other person in my direct team was 100% WFH until recently. She's now in the office 2 days a week, and I noticed all the other people in the office rota'd themselves as WFH those days.
So I have to go in, but she just talks NON-STOP!
Sometimes she's shouting at her laptop
Sometimes in a running commentary on what's she's doing.
Sometimes it's a loud exclamation of "YES! Another one cleared!"
Or she's actually talking at me. But then I quickly realised she has a limited amount of stories as the next time she was in the office, she repeated the entire conversation.
When I'm trying to converse with her, I can see her eyes glaze over whilst she's waiting for me to finish so she can carry on talking.
Now I just stick to "really?" "Wow" "that's nice" etc because I realised she doesn't want to have an actual conversation. She just wants someone to listen to her.
I get barely any work done on the days we're in the office together but my manager just seems happy to have her whole team in the office together.
I think I'm going to try listening to music and maybe when she tells another repeated story, just say "yes you told me yesterday" but she doesn't actually listen to me so not sure it's even worth it.
So, sorry I can't actually help your situation but i empathise.